High‐Entropy Surface Complex Stabilized LiCoO₂ Cathode

Abstract

Elevating the charge voltage of LiCoO 2 increases the energy density of batteries, which is highly enticing in energy storage implementation ranging from portable electronics to e-vehicles. However, hybrid redox reactions at high voltages facilitate oxygen evolution, electrolyte decomposition and irreversible phase change, and accordingly lead to rapid battery capacity decay. Here significantly improved high-voltage cycling stability of Mg-Al-Eu co-doped LiCoO 2 is demonstrated. It is found that element co-doping induces a near-surface high-entropy zone, including an innately thin disordered rock-salt shell and a dopant segregation surface. The high-entropy complex can effectively suppress oxygen evolution and near-surface structure deconstruction. The phase change reversibility between O3 and H1-3 and thermal stability of the cathode are greatly enhanced as well. As a result, the co-doped LiCoO 2 exhibits a remarkable cycling performance, retaining 86.3% and 72.0% of initial capacity over 800 and 2000 cycles, respectively, with a high cut-off voltage of 4.6 V. The feasible co-doping approach broadens the perspective for the development of stable lithium-ion batteries with high operating voltages.

A synergetic promotion of surface stability for high-voltage LiCoO2 by multi-element surface doping: a first-principles study

“…Especially, the surface oxygen loss at high voltage further causes irreversible phase transition or even safety concerns. 13,14 Furthermore, the high-valence O, generated by structural degradation at high voltage, could trigger undesired interfacial side reactions, involving oxidation of the electrolyte. 15,16 Together, these structural degradations and surface parasitic reactions occurring at high voltages will induce serious performance degradation, impeding the practical application of high-voltage LiCoO 2 .…”

Uniform Al Doping in LiCoO2 for 4.55 V Lithium-Ion Pouch Cells

“…For example, a capacity as high as 220 mAh g −1 can be obtained by increasing the charging voltage to 4.6 V. 8−11 However, at a high voltage over 4.5 V, LCO will suffer from severe problems like structural degradation, oxygen release, and parasitic reactions. 12,13 When the charging voltage reaches 4.5 V, an irreversible phase transformation (O3 → H1−3) occurs. 14 The lattice parameters will decrease, and the CoO 2 slab will slip gradually, generating tremendous residual strain inside the particles and further leading to cracks and pulverization of particles.…”

“…LCO exhibits a high theoretical capacity of 274 mAh g –1 , high electronic conductivity, and excellent air stability. , Nevertheless, the charging cutoff voltage of the commercial LCO cathode is limited to 4.45 V (vs Li/Li + ), leading to a discharge capacity lower than 180 mAh g –1 . , It is well known that increasing the charging voltage of LCO can effectively enhance the specific capacity. For example, a capacity as high as 220 mAh g –1 can be obtained by increasing the charging voltage to 4.6 V. − However, at a high voltage over 4.5 V, LCO will suffer from severe problems like structural degradation, oxygen release, and parasitic reactions. , When the charging voltage reaches 4.5 V, an irreversible phase transformation (O3 → H1–3) occurs . The lattice parameters will decrease, and the CoO 2 slab will slip gradually, generating tremendous residual strain inside the particles and further leading to cracks and pulverization of particles.…”

Stabilizing Ni‐rich Single‐crystalline LiNi0.83Co0.07Mn0.10O2 Cathodes using Ce/Gd Co‐doped High‐entropy Composite Surfaces

“…Owing to the TM (transition metal, Ni, Co, and Mn) 3d−O 2p hybridization in Ni‐rich NCM, the Ni, Co, and Mn oxidation states switch between 2 and 2+ x ( x =1–2) during charging/discharging processes, and the hole states are spontaneously created at the O 2p level [4] . Especially, when the operation voltage is higher than 4.3 V, the oxidation of O 2− to O α− (0<α<2) and further extraction of lithium ions (Li + ) from Ni‐rich NCM single crystals result in the increase of hole density in the O 2p orbital [5] .…”